Four in Florida are infected with Zika from local mosquitoes

Health officials in Florida have identified four cases of Zika virus disease that were probably caused by bites from local Aedes aegypti mosquitoes.

The US Centers for Disease Control and Prevention (CDC) said on Friday 29 July that the cases were the first evidence that mosquitoes in the United States have been infected by the virus.

“The bottom line here is that Zika is now present in the continental United States,” said Tom Frieden, CDC director, who warned that other outbreaks in the US should be expected. “Everyone, particularly pregnant women, anywhere, where the Aedes aegypti mosquito is present, should protect themselves against mosquito bites.”

In the US, A aegypti’s range extends across the south and as far north as Connecticut on the east coast and San Francisco on the west coast. A second species capable of transmitting the virus, Aedes albopictus, has a range that extends as far north as Maine and Minnesota.

Frieden said that the cases, in a woman and three men, were first identified in early July 2016 and that transmission seemed to have been limited to a small area involving a few blocks just north of downtown Miami. Since then, Florida officials have conducted an aggressive mosquito abatement effort in the area, which included door to door canvassing to encourage residents to eliminate any standing water where mosquitoes can breed, as well as spraying insecticides from trucks and backpacks to kill adult and larval mosquitoes.

CDC officials said that, judging from the US’s experience with chikungunya and dengue, which are spread by the same mosquito that spreads Zika, the US should expect to see additional individual Zika virus cases and perhaps some small clusters, but not large outbreaks such as those seen in Latin America. This is because of the widespread use of screens, air conditioners, and the relative scarcity of standing water near US residences and businesses, which the Aedes aegypti needs for breeding.

This is not the case, however, in the US territory of Puerto Rico, where many homes and businesses lack screens and air conditioning and where, the CDC reports,1 Zika is spreading rapidly, with nearly 5600 confirmed cases of Zika virus infection reported as of 7 July, including 672 pregnant women. CDC officials suspect that these women represent only a fraction of the pregnant women who have been infected.

“Puerto Rico is in the midst of a Zika epidemic,” said Lyle R Petersen, director of the CDC’s division of vector-borne diseases and incident manager for the agency’s Zika response. “The virus is silently and rapidly spreading in Puerto Rico. This could lead to hundreds of infants being born with microcephaly or other birth defects in the coming year.”